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  • Journal article
    Vitale A, Hennessy MG, Matar OK, Cabral JTet al., 2014,

    Interfacial profile and propagation of frontal photopolymerization waves

    , Macromolecules, Vol: 48, Pages: 198-205, ISSN: 0024-9297

    We investigate the frontal photopolymerization of a thiol–ene system with a combination of experiments and modeling, focusing on the interfacial conversion profile and its planar wave propagation. We spatially resolve the solid-to-liquid front by FT-IR and AFM mechanical measurements, supplemented by differential scanning calorimetry. A simple coarse-grained model is found to describe remarkably well the frontal kinetics and the sigmoidal interface, capturing the effects of UV light exposure time (or dose) and temperature, as well as the front position and resulting patterned dimensions after development. Analytical solutions for the conversion profile enable the description of all conditions with a single master curve in the moving frame of the front position. Building on this understanding, we demonstrate the design and fabrication of gradient polymer materials, with tunable properties along the direction of illumination, which can be coupled with lateral patterning by modulated illumination or grayscale lithography.
  • Journal article
    Xie Z, Pavlidis D, Percival JR, Gomes JLMA, Pain CC, Matar OKet al., 2014,

    Adaptive unstructured mesh modelling of multiphase flows

    , International Journal of Multiphase Flow, Vol: 67, Pages: 104-110, ISSN: 0301-9322

    Multiphase flows are often found in industrial and practical engineering applications, including bubbles, droplets, liquid film and waves. An adaptive unstructured mesh modelling framework is employed here to study interfacial flow problems, which can modify and adapt anisotropic unstructured meshes to better represent the underlying physics of multiphase problems and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control volume and finite element formulation, a 'volume of fluid'-type method for the interface capturing based on a compressive control volume advection method and second-order finite element methods. The framework also features a force-balanced algorithm for the surface tension implementation, minimising the spurious velocities often found in such flows. Numerical examples of the Rayleigh-Taylor instability and a rising bubble are presented to show the ability of this adaptive unstructured mesh modelling framework to capture complex interface geometries and also to increase the efficiency in multiphase flow simulations.
  • Journal article
    Xie Z, Pavlidis D, Percival JR, Gomes JLMA, Pain CC, Matar OKet al., 2014,

    Adaptive unstructured mesh modelling of multiphase flows

    , International Journal of Multiphase Flow, Vol: 67, Pages: 104-110, ISSN: 0301-9322

    © 2013 Elsevier Ltd. Multiphase flows are often found in industrial and practical engineering applications, including bubbles, droplets, liquid film and waves. An adaptive unstructured mesh modelling framework is employed here to study interfacial flow problems, which can modify and adapt anisotropic unstructured meshes to better represent the underlying physics of multiphase problems and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control volume and finite element formulation, a 'volume of fluid'-type method for the interface capturing based on a compressive control volume advection method and second-order finite element methods. The framework also features a force-balanced algorithm for the surface tension implementation, minimising the spurious velocities often found in such flows. Numerical examples of the Rayleigh-Taylor instability and a rising bubble are presented to show the ability of this adaptive unstructured mesh modelling framework to capture complex interface geometries and also to increase the efficiency in multiphase flow simulations.
  • Journal article
    Pavlidis D, Xie Z, Percival JR, Gomes JLMA, Pain CC, Matar OKet al., 2014,

    Two- and three-phase horizontal slug flow simulations using an interface-capturing compositional approach

    , INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 67, Pages: 85-91, ISSN: 0301-9322
  • Journal article
    Percival JR, Pavlidis D, Xie Z, Gomes JLM, Sakai M, Shigeto Y, Takahashi H, Matar OK, Pain CCet al., 2014,

    Control volume finite element modelling of segregation of sand and granular flows in fluidized beds

    , INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 67, Pages: 191-199, ISSN: 0301-9322
  • Conference paper
    Zadrazil I, Matar OK, Markides CN, 2014,

    Phase-locked measurements of gas-liquid horizontal flows

    , American Physical Society - Division of Fluid Dynamics

    A flow of gas and liquid in a horizontal pipe can be described in terms of various flow regimes, e.g. wavy stratified, annular or slug flow. These flow regimes appear at characteristic gas and liquid Reynolds numbers and feature unique wave phenomena. Wavy stratified flow is populated by low amplitude waves whereas annular flow contains high amplitude and long lived waves, so called disturbance waves, that play a key role in a liquid entrainment into the gas phase (droplets). In a slug flow regime, liquid-continuous regions travel at high speeds through a pipe separated by regions of stratified flow. We use a refractive index matched dynamic shadowgraphy technique using a high-speed camera mounted on a moving robotic linear rail to track the formation and development of features characteristic for the aforementioned flow regimes. We show that the wave dynamics become progressively more complex with increasing liquid and gas Reynolds numbers. Based on the shadowgraphy measurements we present, over a range of conditions: (i) phenomenological observations of the formation, and (ii) statistical data on the downstream velocity distribution of different classes of waves.
  • Journal article
    Kovalchuk NM, Trybala A, Starov V, Matar O, Ivanova Net al., 2014,

    Fluoro- vs hydrocarbon surfactants: Why do they differ in wetting performance?

    , ADVANCES IN COLLOID AND INTERFACE SCIENCE, Vol: 210, Pages: 65-71, ISSN: 0001-8686
  • Journal article
    Kuchin IV, Matar OK, Craster RV, Starov VMet al., 2014,

    Influence of the Disjoining Pressure on the Equilibrium Interfacial Profile in Transition Zone Between a Thin Film and a Capillary Meniscus

    , Colloids and Interface Science Communications, Vol: 1, Pages: 18-22, ISSN: 2215-0382

    The behaviour of liquid layers on solid substrates depends on a number of factors, the most important of which is the action of surface forces in the vicinity of the three phase contact line. The equilibrium interfacial (gas/liquid) profile in the transition zone between the thin flat film and the spherical part of a meniscus is determined by the combined action of the disjoining/conjoining and capillary pressures. The disjoining/conjoining pressure is considered to include the electrostatic, van der Waals and structural components. The Poisson–Boltzmann equation is also solved with various boundary conditions to calculate the electrostatic component of the disjoining/conjoining pressure. Wetting conditions are considered and the interfacial profile is determined for various parameters governing the surface interactions, as well as the ratio between the disjoining/conjoining and capillary pressures.
  • Journal article
    Che Z, Fang F, Percival J, Pain C, Matar O, Navon IMet al., 2014,

    An ensemble method for sensor optimisation applied to falling liquid films

    , International Journal of Multiphase Flow, Vol: 67, Pages: 153-161, ISSN: 1879-3533

    Multiphase flow problems are often extremely complex due to their strong nonlinearity. To study multiphase flow, it is important to simulate or measure key parameters accurately, such as pressure drops and flow rates. Therefore, it is essential to place the sensors at the locations with high impact, and to avoid locations with low impact, where impact is determined by a function such as one of the key variables like pressure drop or flow rate. In this paper, an ensemble method is used to optimise sensor locations for falling film problems based on an importance map. The importance map can identify the important regions according to a target function. The sensor locations are selected based on the importance map, the variation of the variables, and the costs of performing the measurements. We demonstrate the approach by applying data assimilation and show that the optimised sensor locations can significantly improve the data assimilation results. Through sensitivity analysis, sensor optimisation, and data assimilation, this study, for the first time, provides a systematic linkage between the experiments and the models for falling film problems. It also presents a new goal or target based method for sensor placement. This method can be extended to other complex multiphase flow problems.
  • Journal article
    Kahouadji L, Witkowski LM, 2014,

    Free surface due to a flow driven by a rotating disk inside a vertical cylindrical tank: Axisymmetric configuration

    , Physics of Fluids, Vol: 26, ISSN: 1070-6631

    <jats:p>The flow driven by a rotating disk at the bottom of an open fixed cylindrical cavity is studied numerically and experimentally. The steady axisymmetric Navier-Stokes equations projected onto a curvilinear coordinate system are solved by a Newton-Raphson algorithm. The free surface shape is computed by an iterative process in order to satisfy a zero normal stress balance at the interface. In previous studies, regarding the free surface deflection, there is a significant disagreement between a first-order approximation [M. Piva and E. Meiburg, “Steady axisymmetric flow in an open cylindrical container with a partially rotating bottom wall,” Phys. Fluids 17, 063603 (2005)] and a full numerical simulation [R. Bouffanais and D. Lo Jacono, “Unsteady transitional swirling flow in the presence of a moving free surface,” Phys. Fluids 21, 064107 (2009)]. For a small deflection, the first-order approximation matches with our numerical simulation and for a large deflection a good agreement is found with experimental measurements.</jats:p>

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